I mounted mine with 4 pieces (one at each corner) of industrial velcro (actually 3M Dual Lock). It allows for removal for cleaning behind, yet holds tightly.
I went this route because I DID NOT want to drill holes for the plate. NY has regular vehicle size plates for a trailer; some states have a MC size plate; still others do not require any plates on this size trailer. I didn't want holes to have to deal with if I move.
I can remove the 3M Dual Lock with WD40 & alcohol.